Be careful of any tropical region. April in Thailand is the hottest I’ve ever been. It really depends on your children and their ages, but I’d carefully consider it.
Get up and out as early as you can to do your activities, particularly if it involves hiking. 10am is when the heat starts to kick in, although in the top end it never goes away.
If your kids have the wrong temperament, or are really suffering, stay in accommodation that has air conditioning. This tip is mostly for those doing the camping experience.
If you start noticing symptoms such as muscle cramps, tiredness, nausea, vomiting – even an altered mental state, head to the AC as soon as you can and start cooling them down.